How to Create a Disk Image in Linux

By Kristen Waters

A disk image is a file that contains an exact copy of your hard disk. The Linux operating system uses the "dd" command to create disk images. The "dd" command copies the hard drive bit by bit, so the disk image is the exact same size as the hard drive. To make the file smaller, you can use the "gzip" command to compress it. To make an image of your main hard drive, you must have a Linux Live CD, such as Knoppix.

Insert the Linux Live CD into your computer's CD drive.

Reboot the system.

Choose the "Boot to CD-ROM" option when prompted.

Make note of the hard drives that are shown on the desktop. The main hard drive has a name similiar to "/dev/sda." The secondary hard drive will has a name similar to "/dev/sdb."

Click the "Terminal" button at the bottom of the screen.

Type the command "su" to switch to the root user. Live CDs do not set up a root user, so you will not be prompted for a password.

Type the command "umount /dev/sda" to ensure that the disk you want to image is not mounted. Replace "/dev/sda" with the device name found in Step 4.

Type the command "mount /dev/sdb /mnt/sdb" to mount the secondary disk drive. Replace "/dev/sdb" with the name of the secondary drive found in Step 4. The second part of the command, "/mnt/sdb," is the directory where the disk will be accessed once it is mounted.

Type the command "dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c > /mnt/sdb/disk.img.gz" to create a compressed image of the original disk. Replace "/dev/sda" with the name of the original drive. Replace "/mnt/sdb" with the name of the directory from Step 8. Replace "disk.img.gz" with the name you want to give the disk image.